The present invention relates to a high-speed radial tire which can improve the permanence of the bead part of the tire and can be used for aircraft and high-speed passenger cars.
In high-speed radial tires such as those for aircraft and for high-speed passenger cars which can run at a high speed exceeding 300 km per hour, recently high-speed radial tires having a belt layer composed of highly elastic belt cords placed outside in the radial direction of carcass of a radial structure in which carcass cords are aligned in the radial direction of a tire have been used.
Since such a tire having a radial structure is constructed with a rigid belt layer, for example, the side-wall part and the bead part deform significantly. Especially due to the construction of a bead apex made of rubber which has a relatively large hardness and generates much heat due to deformation, the bead part develops a high temperature by the heat which is generated from repeated deformations caused by the rolling of the tire. Since it is thicker and since the winding-up portion of the carcass and reinforcement layers are concentrated there, an interlayer shearing strain is generated due to bending deformations, which leads to tire damage.
In the bead part, compression by bending and folding on the rim flange upon loading generates a large compression stress in carcass cords of the bead part, and by repetition of the compression stress, a breakage of the carcass cords and a concentration of stresses generated at the broken edges lower the strength of the carcass cords and the rubber itself, which leads to the damage of the bead part.
Therefore, in order to prevent damage of the bead part, it is preliminarily required to decrease the deformation of the bead.
On the other hand, as shown in FIG. 10, deformation of the bead part is generated by a bending moment M2 which is created by a radial force Fs, which acts on the shoulder part of the tread, acting on the bead part through a bending moment M1 created at the side-wall part of the tread.
Therefore, in order to diminish the bending moment M2 to consequently diminish the deformations of the bead part, it may be considered to increase the internal pressure of the tire, to decrease the rigidity of the side-wall part and to diminish the force Fs which acts on the shoulder part.
However, if the rigidity of the side-wall part is reduced to diminish the bending moment M2 acting on the bead part, the transversal rigidity and the strength of the tire tend to decrease consequently. If the internal pressure is increased, the performance of the tire decreases due to an increased bounce and the balance of the tire becomes worse, which leads rather to shortening of its life.
On the other hand, in a conventional tire, as shown in FIG. 10, the thickness of the shoulder part of the tread Gs has been set to be larger compared with the thickness of the tread part Gc on the equator of the tire CO. As a result, the bending rigidity at the shoulder part becomes larger, which increases, out of the total force F of the ground contact pressure distribution at the ground contact surface, the force Fs acting on the shoulder part relatively, the bending moment M1 and then the bending moment M2.
From this point of view, finding that, in order to decrease the force Fs acting on the shoulder part, by increasing the force Fc at the crown part, out of the load of tire F which is the total force at the ground contact surface, the force Fs at the shoulder part can be relatively decreased. The present inventors have developed this invention. Thus, it is a primary object of the present invention to present a novel high-speed radial tire which can decrease the force Fs acting on the shoulder part and diminish the deformations at the bead part, and hence improve the durability of the bead part.